from the waterfall; or it may be desired to distribute the power in
small amounts at distant points.[1] A method of compressing air by means
of a fall of water has been devised by Mr. Joseph P. Frizell, C.E.,
of St. Paul, Minnesota, which, from the extreme simplicity of the
apparatus, promises to find useful applications. The principle on which
it operates is, by carrying the air in small bubbles in a current
of water down a vertical shaft, to the depth giving the desired
compression, then through a horizontal passage in which the bubbles rise
into a reservoir near the top of this passage, the water passing on and
rising in another vertical or inclined passage, at the top of which it
is discharged, of course, at a lower level than it entered the first
shaft.

[Footnote 1: _Journal of the Franklin Institute_ for September, 1877.]

The formation at waterfalls is usually rock, which would enable the
passages and the reservoir for collecting the compressed air to be
formed by simple excavations, with no other apparatus than that required
to charge the descending column of water with the bubbles of air,
which can be done by throwing the water into violent commotion at its
entrance, and a pipe and valve for the delivery of the air from the
reservoir.

The transfer of power by electricity is one of the problems now engaging
the attention of electricians, and it is now done in Europe in a
small way. Sir William Thomson stated in evidence before an English
parliamentary committee, two years ago, that he looked "forward to the
Falls of Niagara being extensively used for the production of light and
mechanical power over a large area of North America," and that a copper
wire half an inch in diameter would transmit twenty-one thousand horse